Biodiversity & Conservation

CR.MCR.CFaVS.HbowEud

Explanation of sensitivity and recoverability


Physical Factors

Substratum Loss
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Many of the species within the biotope are attached to the substratum or are slow moving so that substratum removal would result in loss of most faunal populations and therefore the intolerance of the biotope is high. With the loss of adult populations, recovery depends upon recolonization by larvae during the breeding season. Recovery by recolonization is likely to be rapid although establishment of the original species composition may require a few years. A recoverability of high is reported - see additional information below for full rationale.
Smothering
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Although the biotope occurs in fairly silty environments, wave sheltered sea lochs, the biotope is usually clear of silt as it occurs on vertical surfaces and/or in strong tidal streams. Smothering by 5cm of sediment is likely to result in the death of many species although some will survive as much of the structure will be above the layer of silt. Feeding structures of the lower parts of hydroids, of sponges and sea-squirts will probably become clogged and suffocate the organisms. Some hydroids, sponges and Alcyonidium diaphanum, will extend above the surface of smothering material and may survive. Hydroids may survive under the silt as stolons even if erect growths are killed. However, some species are likely to be smothered and die so intolerance is assessed as intermediate. Recoverability is assessed as high (see additional information below).
Increase in suspended sediment
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The biotope is found in silty areas in sheltered parts of sea lochs where levels of suspended sediment may increase at times. An increase in suspended sediment may clog respiratory and feeding organs of the suspension feeders in the biotope although food supplies may improve if organic content is high. Most species in the biotope can probably tolerate an increase in suspended sediment at the benchmark level although cleaning costs may increase. The intolerance of the biotope is, therefore, recorded as low. Recovery from the energetic expenditure of clearing the feeding apparatus is likely to take only a few days and so on return to normal conditions recovery will probably be immediate.
Decrease in suspended sediment
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Many of the species in the biotope are suspension feeders so a supply of particles is necessary for feeding. Therefore, a decrease in suspended sediment will reduce food supply which may impair growth. However, effects resulting from a reduction for a month are not likely to be significant so intolerance is assessed as low. On return to normal conditions recovery should be rapid.
Desiccation
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ECR.HbowEud is a circalittoral biotope so desiccation will not be relevant.
Increase in emergence regime
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ECR.HbowEud is a circalittoral biotope so increase in emergence will not be relevant.
Decrease in emergence regime
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ECR.HbowEud is a circalittoral biotope so and decrease in emergence will not be relevant.
Increase in water flow rate
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The biotope is recorded in strong to moderately strong tidal streams. Increased water flow rates may improve the supply of particles, and hence food, to the biotope possibly resulting in increased biomass and abundance of species. However, an increase in water flow at the benchmark level is likely to prevent many of the species feeding and may sweep some poorly attached or unattached species away. Over a period of a year many species are likely to die resulting in an impoverished biotope, or change to another biotope (possibly ECR.CuSH or ECR.BalHpan), and so intolerance is assessed as high. For recovery see additional information below.
Decrease in water flow rate
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Moving water is essential for many reasons, including supplying food and dissolved gases, preventing the accumulation of sediments, and dispersing waste products. The biotope is found in areas of strong to moderately strong tidal streams but, following a decrease at the level of the benchmark, there would still be some flow. Over a period of a year such a reduction in the supply of food particles and the possibility of siltation may cause some decline in abundance of some species (especially passive suspension feeders such as hydroids) but also the ability of others not previously able to settle under stronger tidal flow to settle and survive (possibly more solitary active suspension feeding sea squirts). The biotope therefore becomes less distinctly ECR.HbowEud and may switch to another so intolerance of the biotope is reported to be high. See additional information below for recovery.
Increase in temperature
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Most species in the biotope have a distribution that extends further south than the British Isles, so that long term chronic increases in temperature can probably be accommodated. For hydroids temperature is a critical factor in stimulating or preventing reproduction and most species have an optimum temperature range for reproduction. However, it seems likely that the biotope could tolerate an increase in temperature at the level of the benchmark. It seems that, whilst there may be advantages for some species and disadvantages for others, the biotope will persist and not sensitive is indicated.
Decrease in temperature
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There was no information found on the impact of a decrease in temperature on the biotope. Most species present in the biotope have a distribution that extends to the north of Britain, so that long term chronic decreases in temperature can probably be accommodated. Of the other species particularly common in the biotope there is little information relating to the response to decreasing temperature. For hydroids temperature is a critical factor in stimulating or preventing hydroid reproduction and most species have an optimum temperature range for reproduction. It seems that, whilst there may be advantages for some species and disadvantages for others, the biotope will persist and not sensitive is indicated.
Increase in turbidity
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The biotope is an animal dominated community, dependent on secondary production rather than light and photosynthesis. Therefore, the biotope is probably not sensitive to changes in turbidity and light attenuation. However, light may be important in determining the distributions of a few species through the responses of larvae prior to settlement. Some hydroids, for example, are positively phototactic. There is a general tendency for most hydroids, especially large ones, to be less abundant in well lit situations where competition with algae for the substratum would be greatest although whether this is a direct effect of competition or an evolved avoidance response is not known. Increased turbidity resulting from increased suspended sediment levels may result in some clogging of feeding organs and expenditure of energy in clearing silt. A slight change in the species composition in the biotope will not radically alter the nature of the community. The biotope may extend into shallower, previously algal dominated areas but, on balance, not sensitive is suggested.
Decrease in turbidity
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The most likely impact of decrease in turbidity is to increase light penetration and possibly to encourage algal growth on previously animal dominated surfaces. Light may also be important in determining the distributions of some species through the responses of larvae prior to settlement. There is a general tendency for most hydroids, especially large ones, to be less abundant in well lit situations where competition with algae for the substratum would be greatest although whether this is a direct effect of competition or an evolved avoidance response is not known. However, a slight change in the species composition in the biotope will not radically alter the nature of the community.
Increase in wave exposure
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The biotope occurs in very sheltered conditions so is likely to be intolerant of increased wave exposure. Some of the fine hydroids in the biotope are likely to be damaged. Therefore, an increase in wave exposure for a period of a year is likely to significantly change the nature of the biotope, leading to an increase in wave tolerant species. This will probably result in the development of another biotope and so intolerance is reported to be high. See additional information below for recovery.
Decrease in wave exposure
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The biotope occurs in very sheltered conditions where wave action is minimal or absent and tidal flow is the main source of water movement. Decrease in wave action is consider not relevant.
Noise
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None of the characterizing species are especially sensitive to noise disturbance at the level of the benchmark such as boats etc. passing overhead and so the biotope is recorded as being not sensitive.
Visual Presence
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Most species within the biotope have no or poor visual perception and are unlikely to be affected by visual disturbance such as shading. The biotope is therefore reported as not sensitive to the factor.
Abrasion & physical disturbance
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Most of the species in the biotope are sessile, attached to the substratum and so are unable to move away from an abrasive force or physical disturbance. Hydroids and some of the tunicates are soft and delicate, so abrasion is likely to cause physical damage and possibly death. However, in hydroids the surface covering of hydrorhizae may remain largely intact, from which new uprights are likely to grow. At the level of the benchmark many individuals are likely to be damaged and killed. Thus, intolerance is assessed as intermediate as the biotope is likely to be degraded by physical disturbance. Recovery of the biotope is likely to be high as effects are local and partial - see additional information below.
Displacement
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Many species especially hydroids in the biotope are sessile organisms attached to the substratum that cannot re-attach once removed. A few such as the starfish Asterias rubens are fully mobile whilst others such as the plumose anemone Metridium senile are capable of reattaching whilst sponges such as Halichondria bowerbanki may reattach if they remain in the area, for instance, lodged in crevices. Intolerance is reported to be high as the biotope would be significantly degraded and would probably not be recognizable as ECR.HbowEud. See additional information below for recovery.

Chemical Factors

Synthetic compound contamination
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There is very little information regarding the effect of synthetic chemicals on either the biotope or the individual species in the biotope. Hydroid populations often show sublethal effects of exposure to potential pollutants such as morphological and growth changes (Gili & Hughes, 1995). Following the banning of TBT antifouling paints, the epifauna in the Crouch estuary showed a significant increase in species or abundance of certain species including the ascidian Ascidiella scabra (Rees et al. 2001). Other species frequently found in the biotope such as Alcyonidium diaphanum, Asterias rubens and Metridium senile but also Ascidiella scabra are often found in enclosed areas of ports and harbours where it might be expected that levels of synthetic chemicals might be high. Intolerance is therefore reported to be intermediate suggesting that some mortality of species and reduction of species richness might occur.
Heavy metal contamination
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Information about the effects of heavy metals on the biotope, or the individual species in the biotope, were not found although some general work is available. For example, Bryan (1984) reports that early work has shown that echinoderm larvae are intolerant of heavy metals. In experiments hydroids often show sub-lethal effects of exposure to potential pollutants, such as morphological changes or changes in growth rates. Low concentrations of metal ions may inhibit growth regulators of hydroids and increase growth rates (Gili & Hughes, 1995). It is also well recognized that ascidians are capable of accumulating trace elements such as heavy metals. However, most evidence for heavy metals points only to sublethal effects so it is unlikely that many species would be lost and so intolerance is set to low.
Hydrocarbon contamination
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Species that have been researched and which occur in this biotope are mainly identified as of low intolerance to hydrocarbons. However, Suchanek (1993) notes that Tubularia indivisa, with Eudendrium arbusculuma athecate hydroid, experiences substantial mortality when subjected to only low concentrations of crude oil. Nevertheless, several species characteristic of the biotope occurred on jetty piles adjacent to an oil refinery effluent in Milford Haven (Hiscock et al., 1980-83) and with such equivocal information, a precautionary intolerance assessment of intermediate is given. Recovery is expected to be high (see additional information below).
Radionuclide contamination
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Insufficient information.
Changes in nutrient levels
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There was no information found on the effect of an increase in nutrients on the biotope. However, the general response of communities to an increasing gradient of organic enrichment is one of falling species diversity and an increasing dominance of organisms such as polychaete worms. Such drastic changes however, are usually in response to chronic pollution. At the level of the benchmark, a 50% increase in the nutrients in the biotope, some intolerant species may be lost and growth and reproduction rates of others may be enhanced. If light conditions permit there may be an increase in the abundance of ephemeral algae. The intolerance of the biotope is assessed as low because at the benchmark level impacts are expected to be predominantly sublethal. On return to normal conditions previous growth levels will return very rapidly.
Increase in salinity
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The biotope is found in situations of reduced and low salinity. Increase in salinity may enable other species to colonize and to dominate the community so that the biotope changes, perhaps to ECR.CuSH. An intolerance of high is therefore suggested although rapid recruitment by characterizing species would lead to a high recovery after return to previous levels of salinity assuming that nearby populations of species had survived (see additional information).
Decrease in salinity
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The biotope occurs in reduced salinity which is almost certainly at the lower salinity limit of tolerance for many species. A further decrease in salinity would lead to a loss of species and the biotope would not persist. An intolerance of high is therefore suggested although rapid recruitment by characterizing species would lead to a high recovery after return to previous levels of salinity assuming that nearby populations of species had survived.
Changes in oxygenation
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Cole et al. (1999) suggest possible adverse effects on marine species below 4 mg/l and probable adverse effects below 2mg/l. Some hydroids may be tolerant of deoxygenation. Fulton (1962) found that some polyps of Cordylophora caspia fell off or were reabsorbed after 7 days in the complete absence of oxygen but remaining polyps began feeding shortly after the re-introduction of oxygen and Fulton (1962) concluded that Cordylophora caspia had a low oxygen requirement for growth and was able to grow at oxygen levels of >2mg/l (ca 1.4ml/l). Similarly, the hydroid Melicertum octocostatum annually over-summers as stolons in anoxic conditions in Abereiddy Quarry, growing back in autumn (Hiscock & Hoare, 1975). Sagasti et al. (2000) reported that epifauna communities, including dominant species such as the bryozoans Conopeum tenuissimum and Membranipora tenuis, and the hydroid Obelia bicuspidata were unaffected by periods of moderate hypoxia (ca 0.35 -1.4 ml/l) and short periods of hypoxia (<0.35 ml/l) in the York River, Chesapeake Bay. Their study suggests that estuarine epifaunal communities are relatively tolerant of hypoxia. Although no information could be found on the effects of reduced oxygen on the biotope it is possible that some species will be affected and the biotope degraded so intolerance is reported to be intermediate.

Biological Factors

Introduction of microbial pathogens/parasites
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Although many species may be host to symbiotic or parasitic organisms there was no information found on any diseases affecting the biotope. However, there is insufficient evidence to make an assessment.
Introduction of non-native species
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Of the non-native species known from British waters (Eno et al., 1997), only the ascidian Styela clava is recorded once as occurring in the biotope. However, this is unlikely to change the overall nature of the biotope as Styela clava generally occurs attached by a small base and does not occupy space. The biotope is therefore not intolerance of currently occurring non-native species.
Extraction
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It is extremely unlikely that any of the species indicative of sensitivity would be targeted for extraction and we have no evidence for the indirect effects of extraction of other species on this biotope. Furthermore, the biotope occurs in areas where dredging may be difficult because bedrock predominates.

Additional information icon Additional information

Recoverability
Many of the species that occur in and characterize this biotope are known to settle rapidly and grow quickly. For instance, refer to MarLIN reviews for Metridium senile, Balanus crenatus and Ascidiella scabra) and reviews of epifaunal turf dominated habitats for detail (e.g. £CR.Bug£ and £MCR.Flu£). Recoverability is therefore expected to be high.

This review can be cited as follows:

Hiscock, K. 2002. Halichondria bowerbanki, Eudendrium arbusculum and Eucratea loricata on reduced salinity tide-swept circalittoral mixed substrata. Marine Life Information Network: Biology and Sensitivity Key Information Sub-programme [on-line]. Plymouth: Marine Biological Association of the United Kingdom. [cited 26/10/2014]. Available from: <http://www.marlin.ac.uk/habitatbenchmarks.php?habitatid=45&code=2004>